This invention generally relates to a multi-beam scanning system with a sync signal generation based on a single beam detection and, more particularly, to an image forming apparatus such as a laser printer having a scanning exposure step by a multi-laser beam and a printing step by an electrophotographic process.
Recently, a laser printer having a scanning exposure step by a laser beam and a printing step by an electrophotographic process has been realized.
As a laser printer of this type, a printer adopting a multi-beam scanning system has recently been developed. In this printer, a plurality of beams are generated and a plurality of lines are scanned by these beams, thereby increasing a printing speed.
In such a laser printer, a plurality of beams pass on a single beam detecting section, and a sync signal (horizontal sync signal) in a scanning direction is formed in accordance with a total light amount of the plurality of beams.
However, according to an apparatus described above, the plurality of beams pass on the single beam detecting section, resulting in poor stability of an output waveform.
For example, a position in a main scanning direction is offset, and a jitter is generated in the horizontal sync signal. In this case, components of an image, e.g., vertical lines are distorted, and the quality of especially a very fine image is degraded.